This invention relates to a transfer switch for providing power to the electrical system of a building, such as power supply from a standby generator.
Transfer switches are commonly employed to feed electrical power to selected circuits of a building electrical system during a utility power outage. A transfer switch typically includes a power inlet which is adapted to be electrically interconnected with a power feed from the generator, which supplies power to the transfer switch upon operation of the generator. The transfer switch further includes individual circuit switches which are interconnected with the power inlet and with selected circuits of the building electrical system. During normal operation when power is supplied by a utility or other primary power source, the selector switches are positioned to complete the electrical circuit between the utility power supply and the circuits of the building electrical system. When the primary power supply is discontinued such as during a power outage, or when it is otherwise desired to power selected circuits from an auxiliary power source such as a standby generator, the selector switches are positioned to interrupt the primary power supply circuit and to complete a power supply circuit which includes the auxiliary power source. This functions to supply power to the selected circuits from the auxiliary power source.
The assignee of the present application has developed a number of transfer switch improvements, such as are disclosed in U.S. Pat. No. 5,895,981 issued Apr. 20, 1999 entitled xe2x80x9cGenerator Transfer Panel With A Terminal Arrangement For Establishing A Direct Connection To A Remote Power Inletxe2x80x9d; U.S. Pat. No. 6,163,449 issued Dec. 19, 2000 entitled xe2x80x9cTransfer Switch With Optional Power Inlet And Meter Panelxe2x80x9d; copending application Ser. No. 09/062,257 filed Apr. 17, 1998 (now U.S. Pat. No. 6,293,821 issued Sep. 25, 2001) entitled xe2x80x9cOptional plug Connector For A Transfer Switch Having A Terminal Componentxe2x80x9d; U.S. Pat. No. 6,107,701 issued Aug. 22, 2000 entitled xe2x80x9cOptional Meter Panel For A Transfer Switch Having A Terminal Compartmentxe2x80x9d; U.S. Pat. No. 6,066,817 issued May 23, 2000 entitled xe2x80x9cSocket-Type Circuit Breaker Mounting Systemxe2x80x9d; and copending application Ser. No. 09/692,020 filed Oct. 19, 2000 entitled xe2x80x9cTransfer Switch With Selectively Configurable Cover Structure With Power Input And Meter Capability Separate Power Input And Meter Panelsxe2x80x9d, the disclosures of which are hereby incorporated by reference.
Prior art transfer switches typically utilize single pole double throw selector switches which are acceptable for interconnection in single pole type building electrical circuits. However, there are certain building electrical circuits, such as those associated with a hot water heater or a well pump, which are of a double pole type. In the past, it has been known to tie together a pair of single pole switches for use in switching power in a double pole circuit. This functions to satisfactorily transfer auxiliary power in a double pole circuit.
Prior art transfer switches typically have overcurrent circuit protection in the form of a single pole type circuit breaker interconnected with each single pole selector switch. This arrangement functions satisfactorily to provide circuit protection in single pole type circuits. However, while two interconnected single pole switches function to create a satisfactory double pole switching arrangement for use in a double pole circuit, the overcurrent circuit protection provided by the single pole circuit breakers interconnected with the two single pole switches is a different type of circuit protection than is provided by a double pole circuit breaker.
In addition, prior art transfer switches typically have power supplied directly from the power inlet to the branch circuits, which incorporate single pole circuit breakers. At present, there is an uncertainty in electrical code interpretation as to whether a double pole circuit breaker is required for branch circuit protection.
It is an object of the present invention to provide a transfer switch with a number of enhancements in utility, convenience and circuit protection. Yet another object of the invention is to provide a transfer switch which has enhanced branch circuit protection downstream of the power inlet. Yet another object of the invention is to provide a transfer switch capable of interconnection in double pole branch circuits which includes double pole branch circuit protection. A still further object of the invention is to provide such a transfer switch having circuit connections which can easily be modified for use in either a double pole circuit or a pair of single pole circuits, while providing a compatible type of circuit protection in either case. A still further object of the invention is to provide such a transfer switch which can be modified relatively quickly and easily to provide a double pole switch and circuit breaker arrangement. Yet another object of the invention is to provide such a transfer switch which has a construction and operation generally similar to prior art transfer switches but which incorporates features enhancing use in connection with one or more double pole circuits and which eliminates any uncertainty with requirements pertaining to branch circuit protection.
In accordance with the invention, a transfer switch is adapted for connection between an auxiliary power supply, such as a standby generator, and an electrical load center associated with a building electrical system having a series of electrical circuits. The building electrical circuits include both single pole circuits and double pole circuits. The transfer switch includes a power inlet for supplying power to the transfer switch from the auxiliary power source, typically in the event of a primary power source outage such as a utility power interruption. The transfer switch includes a series of single pole switches and single pole circuit breakers, which are adapted for connection with single pole circuits in the building electrical system.
The transfer switch includes a double pole main circuit breaker connected downstream of the power inlet. The double pole main circuit breaker provides double pole circuit protection for all branch circuits interconnected with the transfer switch.
The transfer switch includes at least one pair of single pole switches which are adapted to be connected together to provide a double pole switch configuration, and a double pole circuit breaker is adapted to be connected in line with the double pole switch formed by the interconnected single pole switches. In one form, the double pole circuit protection is provided by a main circuit breaker connected downstream of the power inlet which provides double pole circuit protection for all single pole branch circuits as well as any double pole branch circuits. In an alternative arrangement, a separate dedicated double pole circuit breaker may be connected in line with an individual double pole branch circuit which is controlled via two single pole switches which are connected together to form a double pole switch, to provide dedicated double pole circuit protection for a double pole circuit.
In either case, double pole circuit protection is provided upstream of the pair of single pole switches which are interconnected to form the double pole switch. The pair of single pole switches can also be used separately in single pole circuit applications, and include single pole circuit breakers which are typically mounted in a socket-type mounting arrangement. When the pair of single pole switches are connected together to form a double pole switch, a double pole circuit breaker is connected in line with the interconnected single pole switches such that the single pole circuit breakers are no longer required. In this case, a conductor member is engaged with the socket-type mounting arrangement for the two single pole circuit breakers, to establish an electrical path between the double pole circuit breaker and the pair of switches which are connected together to form the double pole switch. In a preferred form, the socket-type mounting arrangement defines a pair of aligned side-by-side sockets, each of which is connected in line with one of the switches and is capable of receiving a single pole circuit breaker. The conductor member is configured to fit into the pair of sockets defined by the socket-type mounting arrangement, and includes a pair of separate conductors which engage the socket connections to complete the electrical path between the double pole circuit breaker and the pair of switches. The remaining single pole circuit breakers of the transfer switch are also mounted via a socket-type circuit breaker mounting arrangement, which includes sockets that are arranged in a manner which is incompatible with the conductor member. In this manner, the conductor member can only be used in connection with the specific mounting arrangement associated with the specific pair of switches which are interconnected together to form a double pole switch and which are used in combination with a double pole circuit breaker.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.